1. Field of the Invention
The present invention relates to a liquid droplet ejection head, a liquid droplet ejection device and an image forming apparatus, and more particularly, to a liquid droplet ejection head, a liquid droplet ejection device and an image forming apparatus in which cross-talk is prevented between pressure chambers that are driven consecutively at short time intervals in a liquid droplet ejection head in which nozzles are arranged at high density.
2. Description of the Related Art
Inkjet recording apparatuses (inkjet printers) having an inkjet head (liquid droplet ejection head) in which a plurality of nozzles are arranged, are known in the prior art as image forming apparatuses. An inkjet recording apparatus of this kind forms images by forming dots on a recording medium, by ejecting ink as droplets from nozzles, while causing the inkjet head and the recording medium to move relatively to each other.
Various methods are known conventionally as ink ejection methods for an inkjet recording apparatus of this kind. For example, one known method is a piezoelectric method, where the volume of a pressure chamber (ink chamber) is changed by causing a diaphragm plate forming a portion of the pressure chamber to deform due to deformation of a piezoelectric element (piezoelectric actuator), ink being introduced into the pressure chamber from an ink supply channel when the volume is increased, and the ink inside the pressure chamber being ejected as a droplet from the nozzle when the volume of the pressure chamber is reduced. Another known method is a thermal inkjet method where ink is heated to generate a bubble in the ink, and ink is then ejected by means of the expansive energy created as the bubble grows.
In an inkjet recording apparatus, one image is represented by combining dots formed by ink ejected from the nozzles. In this case, high image quality is achieved by reducing the nozzle diameter and arranging the nozzles at high density, in such a manner that the ink dots deposited by the nozzles become smaller in size and the number of pixels per image is increased.
However, if nozzles are arranged at high density, then there is a danger that cross-talk may arise between nozzles, particularly those which are located close together, in such a manner the ink ejection operation of one nozzle affects the ink ejection operation of the other nozzles. Therefore, in the prior art, various proposals have been made in order to prevent cross-talk of this kind between adjacently positioned nozzles.
For example, it is known that nozzles corresponding to adjacent dots can be divided into a plurality of nozzle rows and arranged in a staggered matrix, in order to prevent cross-talk between adjacent nozzles. Japanese Patent Application Publication No. 2002-103604 discloses an inkjet head in which nozzles are arranged in a matrix fashion, a plurality of nozzle rows arranged in a substantially perpendicular fashion to the printing direction are formed on the same ink supply channel, and adjacent nozzles at the respective orifice hole positions in these nozzle rows are arranged in such a manner that they are staggered by a displacement of δ=h/(n×m) in the printing direction, where h is an integer not less than 2, n is the dot density, and m is an integer not less than 5. Moreover, driving signals are sequentially applied to the respective nozzles in such a manner that the displacement of the nozzles is compensated while separating the application timing to mutually adjacent nozzles.
Furthermore, for example, a method is known in which cross-talk is prevented by applying an auxiliary drive signal to the piezoelectric elements other than the piezoelectric element that is performing an ejection operation, in such a manner that the volume displacement of the other ink chambers can be suppressed. Japanese Patent Application Publication No. 11-157056 discloses a method which suppresses the displacement of the restrictor plates corresponding to the piezoelectric elements other than the piezoelectric element performing an ejection operation, by applying a drive signal of the same phase to the piezoelectric elements that are adjacent to the piezoelectric element performing an ejection operation, while applying a drive signal of reverse phase to the piezoelectric elements separated respectively by one element from the piezoelectric element performing the ejection operation.
As described above, when printing at high image resolution by reducing the dot pitch in order to achieve high image quality, it is important to reduce the nozzle pitch, but this pitch reduction has been constrained by the size of the pressure chambers. Conventionally, high nozzle density is achieved by arranging pressure chambers in an oblique two-dimensional array (a staggered array), but if nozzles which are adjacent due to the dot density and nozzle pitch perform ejection at substantially the same time, then a problem arises in that cross-talk occurs between the adjacent nozzles. Therefore, the development of an inkjet recording apparatus which prevents cross-talk has been sought.
However, in the method disclosed in Japanese Patent Application Publication No. 2002-103604, although cross-talk is prevented by arranging nozzles which consecutively perform ejection at a large distance apart, due to the dot density, it is not always possible to completely avoid simultaneous ejection, and therefore the occurrence of cross-talk cannot be completely prevented.
Furthermore, in the method disclosed in Japanese Patent Application Publication No. 11-157056, an auxiliary drive signal is applied to the other piezoelectric elements apart from the piezoelectric element performing an ejection operation, in such a manner that the volume displacement of the other ink chambers can be suppressed; however, it is not possible to prevent interference in the ink between two ink chambers that share the same supply restrictor for supplying ink to the ink chambers.